In the conventional liquid crystal display device including a backlight for emitting light from the back side of a liquid crystal panel, an image is displayed on the liquid crystal panel by the light emitted from the backlight. In such a liquid crystal display device, the liquid crystal panel includes a pair of transparent substrates, a liquid crystal material interposed between the pair of transparent substrates, and a pair of polarizing plates provided on the front side and back side of the liquid crystal panel. The polarization state of the light incident to the liquid crystal material is changed by the pair of polarizing plates.
In this configuration, when the light is emitted from the backlight, linearly polarized light in the absorption axis direction of the polarizing plate is absorbed by the polarizing plate on the back of the liquid crystal display panel. Thus, in order to increase the brightness while reducing power consumption, there has been proposed a technique (see, for example, JP-A No. 298634/2007) in which a reflective polarizing plate is provided between the back-side polarizing plate and the backlight. The linearly polarized light in the absorption axis is previously reflected in the direction of the backlight by the reflective polarizing plate. Then, the reflected light is reflected again by the liquid crystal panel. In this way, the linearly polarized light in the absorption axis direction is reused. Here, the linearly polarized light in the absorption axis direction is the same meaning as the linearly polarized light having a vibrating surface in the absorption axis direction.
The reflective polarizing plate described in JP-A No. 298634/2007 has a laminate configuration in which a light scattering film is laminated on the light incident side of the reflective polarizer. The light scattering film is laminated so that the transmission axis of the reflective polarizer is parallel to a given direction in the film plane of the light scattering film.
The polarization component necessary for liquid display is transmitted through the light scattering film in the given direction. Then, the polarization component is also transmitted through the reflective polarizer in the transmission axis direction.
On the other hand, of the polarization components not used for liquid display, the linearly polarized light transmitted in the direction perpendicular to the given direction of the light scattering film is reflected in the orthogonal direction of the transmission axis of the reflective polarizer, and is returned again to the light scattering film. The polarization component incident again in the X direction of the light scattering film is scattered backward on the side of the reflective polarizer. As a result, the scattered light is depolarized. Then, the depolarized light is input again to the reflective polarizer.
The linearly polarized light in the transmission axis direction of the reflective polarizing plate is transmitted, and the linearly polarized light orthogonal to the transmission axis is reflected again and returned in the direction of the light scattering film. This process is repeated to increase the amount of light input to the liquid crystal cell.
However, in the liquid crystal display device including the reflective polarizing plate of JP-A No. 298634/2007, there is no consideration of the linearly polarized light that is transmitted through the back-side polarizing plate, and then reflected in the direction of the backlight by the back side of the liquid crystal panel, such as the wiring of the liquid crystal panel. The linearly polarized light even in the transmission axis direction in the backlight is also depolarized in a similar way to the linearly polarized light in the absorption direction that is reflected by the reflective polarizing plate. This reduces the reuse efficiency of the light reflected by the back side of the liquid crystal panel. As a result, the power supply must be increased to increase the brightness.